1. Field of the Invention
The present invention relates to methods and compositions for sealing pipe strings in well bores, and more particularly, to such methods and compositions wherein the well bores penetrate formations which readily fracture at low hydrostatic pressures.
2. Description of the Prior Art
Sealing compositions are commonly utilized in oil, gas and water well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby strings of pipe such as casing are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior of a string of pipe disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe in the well bore and bonds the pipe to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
In some well locations, the subterranean zones or formations into or through which wells are drilled have high permeabilities and low compressive and tensile strengths. As a result, the resistances of the zones or formations to shear are low and they have very low fracture gradients. When a well fluid such as a hydraulic cement composition is introduced into a well bore penetrating such a subterranean zone or formation, the hydrostatic pressure exerted on the walls of the well bore can exceed the fracture gradient of the zone or formation and cause fractures to be formed in the zone or formation into which the cement composition is lost. While light weight cement compositions have been developed and used, i.e., non-foamed cement compositions having densities as low as about 10 pounds per gallon, subterranean zones or formations are still encountered which have fracture gradients too low for even the light weight cement compositions to be utilized without the formation of fractures and the occurrence of lost circulation problems.
Thus, there are needs for improved methods and ultra-low density sealing compositions for sealing pipes such as casings and liners in well bores which penetrate zones or formations having very low fracture gradients.
The present invention provides methods and ultra-low density sealing compositions for sealing pipe in well bores penetrating zones or formations having low fracture gradients which meet the needs described above and overcome the deficiencies of the prior art. The methods of this invention basically comprise the steps of providing a hardenable ultra-low density sealing composition comprised of an epoxide containing liquid, a hardening agent for hardening the epoxide containing liquid, an optional hardening accelerating agent, an optional organosilane bonding agent, a light weight filler and hollow glass microspheres present in an amount sufficient to produce a sealing composition density in a range of from about 5 to about 8.5 pounds per gallon. The sealing composition is placed into the annulus between a pipe and the walls of the well bore and the sealing composition is then allowed to harden. Upon hardening, the sealing composition eliminates the permeability of the zone or formation, increases its strength and resistance to failure and seals the exterior surface of the pipe to the walls of the well bore.
An ultra-low density sealing composition of this invention is basically comprised of an epoxide containing liquid, a hardening agent for hardening the epoxide containing liquid, an optional hardening accelerating agent, a light weight filler and hollow glass microspheres present in an amount sufficient to produce a sealing composition having an ultra-low density in the range of from about 5 to 8.5 pounds per gallon. The ultra-low density sealing compositions can also include an organosilane bonding agent.
It is, therefore, a general object of the present invention to provide methods and ultra-low density sealing compositions for sealing pipe in well bores.
Other and further objects, features and advantages of the present inventions will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
As mentioned, oil, gas and water wells are often drilled into subterranean zones or formations having high permeabilities and low resistances to failure. When conventional well sealing fluids enter such zones or formations by way of the well bores penetrating them, the fracture gradients of the zones or formations can often be exceeded. As a result, fractures are formed in the zones or formations and the sealing fluids are lost therein. In many cases, the fracture gradients of the formations are so low that wells drilled into the formations cannot be completed and must be abandoned. The term xe2x80x9cfracture gradientxe2x80x9d is used herein to mean the hydraulic pressure per unit of depth required to be exerted on a subterranean formation to cause fractures therein.
By the present invention, methods and ultra-low density sealing compositions are provided for sealing pipes in well bores penetrating zones or formations which readily fracture at low hydrostatic pressures e.g., hydrostatic pressures as low as 10 pounds per gallon. The methods of this invention for sealing a pipe in a well bore penetrating a zone or formation which readily fractures at low hydrostatic pressures is basically comprised of providing a hardenable ultra-low density sealing composition comprising an epoxide containing liquid, a hardening agent for hardening the epoxide containing liquid, an optional hardening accelerating agent, a light weight filler and hollow glass microspheres present in an amount sufficient to produce a sealing composition density in the range of from about 5 to about 8.5 pounds per gallon. The sealing composition is placed into the annulus between the exterior surfaces of the pipe and the walls of the well bore and the sealing composition is allowed to harden therein. As mentioned above, the sealing compositions of this invention can optionally include an organosilane bonding agent to increase the ability of the sealing composition to provide a strong bond to the pipe and to the walls of the well bore.
A variety of hardenable epoxide containing liquids can be utilized in accordance with this invention. Examples of preferred such hardenable epoxide containing liquids include, but are not limited to the diglycidyl ether of 1,4-butanediol, the diglycidyl ether of neopentyl glycol, the diglycidyl ether of cyclohexanedimethanol and mixtures thereof. Of these, the diglycidyl ether of cyclohexanedimethanol is the most preferred.
A suitable epoxide containing liquid comprised of the diglycidyl ether of 1,4-butanediol is commercially available from the Shell Chemical Company under the trade name xe2x80x9cHELOXY(copyright)67xe2x80x9d. This epoxide containing liquid has a viscosity at 25xc2x0 C. in the range of from about 13 to about 18 centipoises, a molecular weight of 202 and a 1-gram equivalent of epoxide per about 120 to about 130 grams of the liquid. A suitable diglycidyl ether of neopentyl glycol is commercially available from Shell Chemical Company under the trade name xe2x80x9cHELOXY(copyright)68xe2x80x9d. This epoxide containing liquid has a viscosity at 25xc2x0 C. in the range of from about 13 to about 18 centipoises, a molecular weight of 216 and a 1-gram equivalent of epoxide per about 130 to about 140 grams of the liquid. A suitable diglycidyl ether of cyclohexanedimethanol is commercially available from Shell Chemical Company under the trade name xe2x80x9cHELOXY(copyright)107xe2x80x9d. This epoxide containing liquid has a viscosity at 25xc2x0 C. in the range of from about 55 to about 75 centipoises, a molecular weight of 256 and a 1-gram equivalent of epoxide per about 155 to about 165 grams of the liquid.
A variety of hardening agents can also be utilized in the sealing compositions of this invention containing the above described epoxide containing liquids including, but not limited to, aliphatic amines, amide amines, amido amines, imidazoles, aliphatic tertiary amines, aromatic amines, cycloaliphatic amines, heterocyclic amines, polyamides, polyethylamines and carboxylic acid anhydrides. Of these, aliphatic amines, aromatic amines and carboxylic acid anhydrides are the most suitable.
Examples of aliphatic and aromatic amine hardening agents are triethylenetetraamine, ethylenediamine, N-cocoalkyltrimethylenediamine, isophoronediamine, diethyltoluenediamine and tris(dimethylaminomethylphenol). Examples of suitable carboxylic acid anhydrides are methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride, polyazelaic polyanhydride, phthalic anhydride and mixtures of two or more of such hardening agents. Of these, triethylenetetraamine, ethylenediamine, N-cocoalkyltrimethylenediamine, isophoronediamine, diethyltoluenediamine and tris(dimethylaminomethylphenol) are preferred, with tris(dimethylaminomethylphenol) being the most preferred. The hardening agent or mixture of hardening agents utilized are included in the compositions of this invention in an amount in the range of from about 15% to about 40% by weight of the epoxide containing liquid in the composition.
Various hardening accelerating agents can be utilized including, but not limited to, triethanolamine, benzylalcohol, nonylphenol and tris(dimethyl aminoethanol) phenol. Of these, tris(dimethyl aminoethanol)phenol is preferred. The hardening accelerating agent is included in the sealing composition of this invention in an amount in the range of from about 0% to about 10% by weight of the epoxide containing liquid therein.
Various lightweight fillers can also be utilized including, but not limited to, diatomaceous earth, fumed silica and amorphous silica. Of these, amorphous silica is preferred. A suitable amorphous silica filler is commercially available from Halliburton Energy Services, Inc. of Duncan, Okla. under the trade name xe2x80x9cSILICALITE(trademark)xe2x80x9d. The lightweight filler used is included in the sealing composition in an amount in the range of from about 2.5% to about 30% by weight of the epoxide containing liquid in the composition.
The hollow glass microspheres are preferably synthetic hollow glass microspheres, which are commercially available from Minnesota, Mining and Manufacturing Co. (3M(trademark)) under the trade name xe2x80x9cSCOTCHLITE(trademark)xe2x80x9d. These very low density microspheres are formed of a chemically stable soda-lime borosilicate glass composition which is non-porous and does not absorb epoxide containing liquid. The hollow glass microspheres are included in a sealing composition of this invention in an amount sufficient to produce a sealing composition density in the range of from about 5 to about 8.5 pounds per gallon, i.e., in an amount of about 15% to about 45% by weight of the epoxide containing liquid in the sealing composition.
As mentioned, the ultra-low density sealing composition can also include an organosilane bonding agent. The organosilane bonding agent is preferably 3-aminopropyltrimethoxysilane or N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, which are commercially available from Witco Corporation under the tradenames A-1102 and A-1120, respectively. When used, the orgonaosilane bonding agent is preferably included in the sealing composition in an amount in the range of from about 0% to about 5% by weight of the epoxide containing liquid in the sealing composition, more preferably about 1%.
A preferred method of this invention for sealing pipe in a well bore penetrating a zone or formation which readily fractures at low hydrostatic pressure is comprised of the steps of:
(a) providing a hardenable ultra-low density sealing composition comprised of an epoxide containing liquid, a hardening agent for hardening the epoxide containing liquid, an optional hardening accelerating agent, a light weight filler and hollow glass microspheres present in an amount sufficient to produce a sealing composition density in the range of from about 5 to about 8.5 pounds per gallon;
(b) placing said sealing composition into the annulus between said pipe and the walls of said well bore; and
(c) allowing said sealing composition to harden.
A more preferred method of the present invention for sealing pipe in a well bore penetrating a zone or formation which readily fractures at low hydrostatic pressure is comprised of the steps of:
(a) providing a hardenable ultra-low density sealing composition comprised of the diglycidyl ether of cyclohexanedimethanol, a hardening agent comprised of tris(dimethylaminomethylphenol), a hardening accelerating agent comprised of tris(dimethylaminoethanol)phenol, a light weight filler comprised of amorphous silica an organosilane bonding agent comprised of 3-aminopropyltriethoxysilane or N-2-(aminoethyl)-3-aminopropyltrimethoxysilane and synthetic hollow glass microspheres present in an amount sufficient to produce a sealing composition density in the range of from about 5 to about 8.5 pounds per gallon;
(b) placing said sealing composition into the annulus between said pipe and the walls of said well bore; and
(c) allowing said sealing composition to harden.
A preferred ultra-low density sealing composition of this invention for sealing pipe in a well bore penetrating a zone or formation, which readily fractures at low hydrostatic pressure is comprised of:
(a) an epoxide containing liquid;
(b) a hardening agent for hardening the epoxide containing liquid present in the sealing composition in an effective amount;
(c) an optional hardening accelerating agent present in the sealing composition in an effective amount;
(d) a light weight filler present in the sealing composition in an effective amount; and
(e) hollow glass microspheres present in the sealing composition in an amount sufficient to produce a sealing composition density in the range of from about 5 to about 8.5 pounds per gallon.
A more preferred ultra-low density sealing composition for sealing pipe in a well bores penetrating a zone or formation which readily fractures at low hydrostatic pressures is comprised of:
(a) an epoxide containing liquid comprised of the diglycidyl ether of cyclohexanedimethanol;
(b) a hardening agent comprised of diethyltoluenediamine present in the sealing composition in an amount in the range of from about 15% to about 40% by weight of the epoxide containing liquid therein;
(c) a hardening accelerating agent comprised of tris(dimethylaminoethanol) phenol present in the sealing composition in an amount in the range of from about 0% to about 10% by weight of the epoxide containing liquid therein;
(d) a light-weight filler comprised of amorphous silica present in the sealing composition in an amount in the range of from about 2.5% to about 30% by weight of the epoxide containing liquid therein;
(e) an organosilane bonding agent comprised of 3-aminopropyltriethoxysilane or N-2-(aminoethyl)-3-aminopropyltrimethoxysilane present in the sealing composition in an amount in the range of from about 0% to about 5% by weight of epoxide containing liquid therein; and
(f) synthetic hollow glass microspheres present in an amount sufficient to produce a sealing composition density in a range of from about 5 to about 8.5 pounds per gallon.
In order to further illustrate the methods and compositions of this invention, the following examples are given.